I have a pretty reliable in-line that is set up for caps.....I think it is able to be converted to 209's and if so...I won't hesitate.
I do have a very traditional sidelock, and though I have a kit which could convert it to use small rifle primers....I'm gonna leave it original.....its just more fun in a way to do it the "harder" way.
209's are by far more reliable, easier to maintain, and consistent in the intitial charge they throw.